A new study reveals that the rare species of seals living in Antarctica make sounds outside the range of human hearing.
By Racheli Vox, Angle - a news agency for science and the environment
Those who have never heard a seal can easily be mistaken and think that it is a sound from another world. "When we dived near them, we occasionally heard a sound that starts as a high-pitched whistle, descends to low frequencies and ends with a series of 'pulses' that shake the entire body of water," says Dr. Danny Kerem from the Institute of Marine Studies and the Maurice Kahn Marine Research Station at the School of Marine Sciences Rani at Haifa University. "This is a one-time and recommended experience."
However, it turns out that our limited human ears are only able to hear part of the story. In a new American-Canadian study recently published it was revealed that seals from a small species (Leptonychotes weddellii) make sounds that were previously unknown - and that are outside the range of human hearing.
Whale seals are large marine mammals that live in Antarctica. Their length can reach to 3 meters And their weight is about 500-400 kilograms. They spend most of their time Under water, and in winter, when ice covers the sea, they make holes in it with their teeth and rise through them to the surface of the water to breathe.
In a study conducted in 1982 34 different types of complex calls have been identified that seals and seals make, all within human hearing range. The explanation was that they are used for social communication. The seals' calls that humans can hear consist of chirps, whistles, hums and rattles, and can be heard even when the animal is underwater and the listener is outside of it.
Tweet at 50 kHz
The new sounds, the details of which were published in the scientific journal Journal of the Acoustical Society of America, were discovered with the help of underwater recording equipment installed in the depths of the Ross Sea in Antarctica, which regularly recorded the sounds of the seals. The staff members of McMurdo Station, the nearby American research station, to which the recordings were broadcast, used to play the familiar sounds of the seals in the researchers' dormitories at night, and the enchanted sounds accompanied the researchers into sleep. Over time, the researchers discovered that the sensitive recording equipment also recorded sounds that their own ears could not hear.
The sounds the researchers discovered are supersonic: that is, their frequency is too high to be heard by the human ear. The range of human hearing is limited to sounds whose frequencies are in the range between 0.02 and 20 kilohertz (as with age the ability to hear high frequencies weakens). However, some other animals, such as dogs, bats and dolphins, are also able to hear higher frequencies.
In the new study, the researchers found that the seals vocalize Nine types of readings, which were not known until now. Each of them includes one or more vocal components - among them chirps, whistles and curls. The average frequencies of 11 of these sound components are higher than 20 kHz, and the frequencies of six of them are higher than 21 kHz throughout. The average frequencies of two of the vocal components are even higher than 30 kHz. The frequency of one of the discovered whistles reaches 44.2 kHz, and one of the tweets starts at no less than 49.8 kHz. The frequencies of the overtones (the higher tones that accompany the main tone in natural voices and musical instruments and that dictate the tone of the voice) of some of the readings were higher than 200 kHz.
A recording of the seals singing:
According to Kerem, it makes sense that the seals make sounds in the ultrasonic frequency range. "The hearing range of seals extends towards higher frequencies than ours, and they hear well at least up to 60-50 kHz," he says. "Therefore, it is no wonder that they produce sounds that extend to the upper end of their good hearing range."
Voice navigation in total darkness
Why do the seals make the newly discovered sounds? Good question. According to the researchers, it is possible that this is social communication, and that the use of relatively high frequencies allows the seals to stand out above all the other "noise" in their environment - in the night of the lower sounds made by other animals.
However, in Kerem's opinion, the likelihood that this possibility is true is not high, this is because Wedel seals do not deal with a lot of "noise" in their living environment. "This species spends most of its time in areas where the ice is thick, close to land, where only it is able to make holes in the ice with its teeth," he says. "Unlike him, all the other species that are unique to Antarctica must have free access to the sea, so in the cold season they migrate out with the outer edge of the ice shelf that floats on the sea."
Another possible use of the sounds proposed by the researchers is for the purpose of performing echolocation (echolocation): making sounds and listening to the echoes that return to them from their surroundings as a result, with the aim of identifying the objects that surround them, navigating, looking for food, and the like. Various animals make use of this ability of biological sonar, including bats as well as other marine mammals, such as dolphins and toothed whales. If the newly found sounds are indeed used by the seals for echolocation, this may explain how they are able to navigate and find food in the total darkness that prevails in Antarctica in winter, when the sun does not shine all day long.
According to Kerem, this possibility is most likely. "I had the privilege of diving under the ice in Antarctica, through a hole that the seals made and that we widened," he says. "In daylight, the feeling is like diving into a crystal palace, and you can easily notice where the ice is thin and thus understand how to reach the hole through which you can get out. In total darkness, on the other hand, the situation is completely different, so it is very likely that the seals use high-frequency chirps to navigate towards the holes in the ice."
Do not make noise near the seals
According to Kerem, the new research and a better understanding of the seals' communication frequencies are important when it comes to the possibility that human activity in their area will cause disturbance or damage. "If human noise introduced into the water overlaps in frequency with the hearing frequency of the animal, this may damage communication, disturb and drive away, and at high intensities cause temporary or permanent deafness in the range in question," he says. A positive point is that, unlike what happens in many other areas of the world, human activity in the habitats of seals and seals is minimal, which reduces the chances of harming them.
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